1. Field of the Invention
The present invention generally relates to image forming and, more particularly, to a process cartridge removably loadable on an image forming apparatus, and the image forming apparatus equipped with the process cartridge.
2. Description of the Related Art
Conventionally, image forming apparatuses using the electrophotographic image forming process have employed the process cartridge system, in which a photosensitive drum and a process means are integrally combined into a cartridge so as to be removably loadable onto an image forming apparatus. A process cartridge that includes a development means, and a process cartridge that does not include a photosensitive drum but includes only a development means as a process means (i.e., development cartridge) are provided with a toner seal for sealing and closing an opening of a developer container containing a toner so as to prevent the toner from scattering during, for example, transportation of the cartridge. This toner seal should be removed by the time when image formation is started after the cartridge is loaded on a main body of an image forming apparatus. Only if the seal is pulled out by a user before the cartridge is loaded on an image forming apparatus, the toner can be supplied to a development sleeve.
However, a user may insert the cartridge in an image forming apparatus while forgetting to pull out the toner seal, if the cartridge is configured in such a manner that the cartridge can be loaded on the image forming apparatus even with the toner seal still attached thereto. With the toner seal remaining on the cartridge, the toner is never supplied to a development sleeve, and therefore printing in a print sheet becomes impossible, resulting in a discharge of a blank sheet. If the user does not stay near the image forming apparatus, the user cannot find that he has forgotten to remove the toner seal. As a result, the image forming apparatus may continue discharging blank paper without anything printed thereon.
As a possible solution to solve this problem, there is proposed the method of determining the presence or absence of a toner seal by utilizing electrostatic capacity between a development sleeve and an antenna. Japanese Patent Application Laid-Open No. 2003-208002 discusses that electrical insulation is provided with use of an insulating toner seal to a contact between an antenna configured to output current corresponding to the above-mentioned electrostatic capacity and a detection circuit at a main body of an image forming apparatus. Due to this configuration, the detection circuit outputs a detection result of a zero level when the toner seal is not pulled out, thereby enabling a notification to a user that the user has forgotten to pull out the toner seal. Further, the image forming apparatus can be configured so as to detect a remaining amount of the toner based on the electrostatic capacity between the development sleeve and the antenna, if the toner seal is pulled out.
However, in the invention discussed in Japanese Patent Application Laid-Open No. 2003-208002, the detection circuit also outputs a detection result of a zero level, when the cartridge is not loaded on the main body of the image forming apparatus. Therefore, when the detection circuit outputs a zero-level detection result, it cannot be determined whether this indicates that the cartridge is not loaded on the image forming apparatus or that the toner seal is not removed. Therefore, the image forming apparatus should have another detection means such as a photosensor capable of detecting a protrusion of a cartridge to detect the presence or absence of the cartridge.